Three-phase AC phase sequence has critical impacts on whether a three-phase powered device can normally operate or not. Usually, a three-phase AC power source of the three-phase powered device requires positive sequence (as shown in FIG. 1) rather than negative sequence (as shown in FIG. 2). Take electrical drive device as an example, once the three-phase AC power source has wrong sequence, it will result in the inverse operation of the electrical drive device, and lead to the fault of the electrical drive device, even be harmful to operators. Hence, it needs to introduce a three-phase AC phase sequence detection and a decision function in the control of electrical drive device.
In the prior art, the three-phase AC phase sequence is determined by extracting angular frequency information of three-phase AC and determining the angular frequency information. Though the above method can achieve a precise detection of phase sequence, since it needs to extract the angular frequency information of three-phase AC and there are a feedback circuit and an adjustment of error signal during the process of angular frequency extraction, the control system is complicated.